The conventional robots were generally specialized for specific functions, but there is a growing demand for robots which are more similar to humans and are given with a greater versatility. In particular, with the advance in the development of CPUs and programming technology, various upright bipedal or otherwise traveling robots have been proposed. Such robots are capable of serving various practical purposes in homes, work places and fairs. Because such robots are intended to perform jobs which are normally performed by humans, it is necessary and desirable for such a robot to be able to access objects which are required for performing such jobs both quickly and accurately.
In particular, when a robot attempts to reach an object in front of it with a fully extended arm, the fact that the arm undergoes an arcuate motion depending on the angular deviation from a horizontal position of the arm makes the arithmetic computation for controlling the fore-and-aft distance between the free end of the arm or the hand and the object in the front highly complex. If the arm length is increased, the problem associated with the arcuate motion of the arm is reduced, but it detracts from the compact design of the robot. Conversely, if the arm length is reduced excessively, the work efficiency is impaired. It is therefore important to determine the length of the arm in a rational way.
Also, if the arm is controlled by fully taking into account the arcuate motion of the arm, the burden on the CPU increases particularly in an upright walking bipedal robot. In the access control of such an arm, it is desirable to minimize the burden on the CPU.